Method for the making of microcrystalline metallic materials

ABSTRACT

Apparatus and process for the manufacturing of microcrystalline metallic materials in band form, wherein the chemical compositing for the cooling roller given in ranges within which the upper surface roughness is reduced, the geometry is improved, the presence of microcracks is eliminated or reduced and the ductibility of the band is increased.

The invention relates to the area of metallurgy and is applicable to themanufacturing of metallurgic ready made products, especially in bandform having microcrystalline, respectively, define crystalline materialstructure.

For the continuous manufacturing of strip materials directly from melts,there are apparatus and methods known, such as for example, for theamorphous soft magnetic materials (D. Egami, AIP Conference Procedure,No. 24, 1975, 697) by a rapid solidification on a rotating roller(spinning melting method).

For the manufacturing of strips having amorphous structure according tosuch process, is characteristic that in a continuous process a perfectgeometric form and the achieving of an applicability for the requiredphysical-technical properties can be obtained only in a limited area oftechnological conditions, which are characteristics for the alloyingprocess used in each case. Regarding the roller material, therequirement for a high heat conductivity at sufficiently goodwettability of the roller upper surface will dominate the situation.This lead to the substantial use of copper and copper alloys.

Strips from Fe-materials having microcrystalline structure areobtainable on such rollers not with a sufficiently good band geometry,that is, with a form constant, upper surface roughness and edgeformation, as well as free from oxidation (scale and startingcoloration). Therefore, for Fe-Cr-Al resistance alloying according to D.Naohara et al (Metal. Trans. 13A 1982, 337) for the manufacturing ofbands a steel roller (without the indication of the steel type) is to beused. The produced band possesses, however, a defective geometry, sothat, for example, no probes can be produced from it for the mechanicaltesting. According to H. A. Davies et al (Procedure of the SecondConference on Rapid Solidification Processing, 1980, Reston, USA) duringmanufacturing of thin bands from Ni-alloys the use of an unalloyed steelis proposed instead of copper for the roller, which will reduce theoxidation on the upper surface of the band, although it will noteliminate it. It is generally known, that the occurrence of oxide layerscan be prevented by performing the process under a protective gas or invacuum. In U.S. Pat. Nos. 4,318,733 and 4,362,553 the production of toolsteels is described by means of spinning melting process. The productionof conventional tool steels is not possible with the help of suchmethods, since such steels do not wet the upper surface of the roller(Cu, respectively, CuBe rollers). As a result, there cannot form astable melt puddle, therefore, undesirable conditions will result for aband formation.

The described tests in these patents show, that the melt jet uponcontacting onto the rotating cooling roller, will become deformed, willbreak off in droplet form and, it will leave the upper surface of theroller in still liquid melt form. As a result, a rapid cooling cannot berealized. A strip production according to the above-mentioned patentsbecomes possible only if Boron is added between 0.5 and 1.5%. This, onthe other hand, is uneconomical since Boron is an expensive alloyingelement.

It is the aim of the invention to improve the quality ofmicrocrystalline bands from metallic materials produced in a rapidsolidification, especially, in spin melting process, and to improveespecially their geometry and their upper surface structure and, at thesame time, to reduce the costs of performing the process.

It is the object of the invention to employ cooling rollers ofappropriate materials and to define the process parameters in dependencefrom the roller material and from the material to be melted in such amanner, that microcrystalline strips from the metallic materials havingan exact geometry and good upper surface charraceristics could beproduced without working under a protective gas or in vacuum.

According to the invention, the above object is solved in that theroller which is to be used in the rapid solidification process with aspinning melt method or the roller upper surface coming into contactwith the melt in a rapid solidification process should be manufacturedfrom a suitable material. As a suitable material, a material should beused which preferably corresponds to the chemical composition of themelt within an error limit of a chemical analysis. Such applicablematerial for the roller material according to the invention is one whichhas a chemical composition as follows: for the base metal of the alloy:±5 weight %, for alloy elements with contents of ±5 weight %: ±10%; foralloy elements with contents of 1-5 weight %: ±20%.

During the maufacturing of microcrystalline strips from a metallicmaterial according to the spinning melt process, the melt is pressedfrom a jet onto the upper surface of a cooling roller which is set inrotation. Under certain process parameters, on the upper surface of thecooling roller a melt puddle will form, from which due to the heatremoval through the roller, a strip will form. For this, it is necessaryto match the materials of the roller upper surface with that of themetal to be melted. Furthermore, the process of the formation of thestrip with the required properties will be aided by an appropriatetemperature of the roller upper surface and by the coordinates of theair rejecting devices and of the band strippers. The air rejectingdevice or air rejector deflects the air layer from the upper surface ofthe roller which has been picked up by the roller due to its rotation.The temperature of the roller upper surface will be between 20° C. and300° C., preferably between 80 and 180. The air rejector will bearranged on about 3-10 mm before the melt puddle. The band stripper willbe set according to the required upper surface quality of the band,whereby an increase in the distance between the melt puddle and the bandstrippers will mean an increase in the after cooling time and, thereby,a reduction of the thickness of the oxide layer on the strip uppersurface. In addition, the known, specially defined process parameters,such as the peripheral speed between 5 and 20 m/s, the press outpressure between 5 and 50 kPa and, the spacing between the nozzle andthe roller between 0.1 and 0.4 mm, are to be observed.

The essence of the invention rests on the novel recognition, that byusing a suitable roller material against other materials, will result ina much improved wetting between the metallic melt and the roller uppersurface. By employing the invention, a microcrystalline band formetallic materials can be produced in contrast to the heretofore knownstate of art of the rapid solidification processes, with a much improvedquality.

The use of the invention will result in the following qualityimprovements:

1. Reduction of the roughness of the band upper and lower side;

2. Improvement of the geometry of the band (homogenous cross section,edge sharpness);

3. Elimination or reduction in the number of the microcracks;

4. Reduction, respectively, a desired setting of the oxidation grade ofthe bands;

5. Increase of the ductility of the band for certain alloys.

The invention will be explained on hand of the following three specialexamples:

EXAMPLE 1

Manufacturing of rapid working steel having a microcrystalline structureaccording to a spinning melt process. The cooling roller possesses achemical composition in its main components as follows:

Tungsten 6.6 weight %; molybdenum 5.2 weight %; chronium 4.0 weight %;vanadium 2.1 weight %; carbon 0.83 weight %, the rest is iron. Thediameter of the roller is 200 mm, the width is 40 mm. The upper surfaceof the roller possesses a average roughness of ±0.15 μm. For deflectingthe air layer carried along during the rotation of the roller, an airrejector is positioned 3 mm before the melt jet contact point.

The alloy to be melted has the following chemical components:

Tungsten 6.35 weight %; molybdenum 5.15 weight %; chromium 3.87 weight%; vanadium 1.98 weight %; carbon 0.82 weight %; the rest is iron.

For the manufacturing of a band according to the above-describedprocess, the following process parameters should be set:

Peripheral speed of the roller: 13 m/s;

Spacing between the nozzle and the roller: 0.15 mm;

Press-out pressure: 25 kPa;

Smelt temperature: 1570° C.

Positioning of the strippers: 450 mm behind the melt jet contact point;

Roller temperature: 120° C.

With the help of such roller made from the specially suitable materialand with the help of the defined positioned air rejector, as well as onhand of the above-described specific process parameters, it was possibleto produce in air a rapid solidified rapid working steel band having amicrocrystalline structure. It is characterized by a very good dimensionretention over its length and width. The average band roughness is about<2 μm. The produced band is in addition completely metallic bright. Itis remarkable that this steel, due to its high carbon contact, tends tooxidize very strongly in air. Such results can be explainedsubstantially by the good wetting properties of the cooling roller whichreflects itself in a very good heat transfer and, also resulting in aleaving temperature of the band from the roller amounting to 540° C.,which lies below the critical temperature range of oxidation.

EXAMPLE 2

Alloyed bands have been manufactured which are composed substantiallyfrom 14.73 weight % of chromium and 5.44 weight % of aluminum and aniron content of about 79 weight %.

The cooling roller is a composite roller, the base body of which is madefrom a Cu-alloy and, the upper surface layer of which is made from amaterial having the following chemical composition in its maincomponents:

About 79% weight Fe; 14.8 weight % chromium and 5.16 weight % aluminium.

The roller has a diameter of about 400 mm and a width of 70 mm. Theaverage roughness of the roller upper surface amounts to ±0.25 μm.

The following process parameters have been set:

Positioning the air rejector 5 mm before the melt jet contact point;

Peripheral speed of the roller: 15 m/s;

Spacing between the nozzle and the roller: 0.2 mm;

Argon gas press-out pressure: 30 kPa;

Temperature of the melt at casting: 1650° C.

Position of the band stripper: 300 mm behind the melt jet contact point;

Roller temperature: 100° C.

With such process parameters on a roller having an upper surface layermade from a suitable material, a metallic bright band of 100 μmthickness has been manufactured in air. Such strip is ductile andpossess a good constant of its geometry and edge quality over the entireband length.

EXAMPLE 3

The alloying, the roller material and the process parameters have beenthe same as in Example 2. By positioning the band stripper between 300and 100 mm behind the melt jet contact point, the leaving temperature ofthe strip from the roller has been set between 600° and 900° C. As aresult, a desired oxidation of the band has been obtained in an oxygenenriched atmosphere. The pre-oxidation increases the use value of theband made from the heat conducting alloy mentioned in Example 2.

We claim:
 1. In a method for the manufacturing of microcrystallinemetallic materials in band form by rapid solidification of a melt in aspinning melt process, comprising contacting the melt with a coolingroller of a material the chemical composition of which lies within anadmissible limit of analysis error of the chemical composition of themelt, wherein said chemical composition of the individual alloy elementsis matching the chemical composition of the melt within the followinglimits:for the base metal of the alloy: ±5 weight %; for alloy elementswith contents of 35 5 weight %: ±10%; for alloy elements with contentsof 1-5 weight %: ±20%.
 2. The process according to claim 1, wherein thecooling roller comprises at least an upper surface layer and a bodyportion, and wherein the chemical composition of the upper surface layercorresponds to the composition recited in claim
 1. 3. Process for themanufacturing of microcrystalline strips, which employs a cooling rollerhaving the properties according to claim 1 wherein the upper surfacetemperature of the cooling roller is kept from 20° C. to 300° C.
 4. Theprocess of manufacturing of microcrystalline strips, which employs acooling roller having the properties according to claim 1 wherein theupper surface temperature of the cooling roller is kept from 80° C. to180° C.
 5. The process for manufacturing microcrystalline strips,employing a cooling roller according to claim 1 wherein an air rejectingdevice is arranged in a distance.
 6. The process of manufacturingmicrocrystalline strips, employing a cooling roller according to claim 1wherein the leaving temperature of the strip is set by the positioningof a stripper.